This application claims the priority benefit of Taiwan application serial no. 89104697, filed Mar. 15, 2000.
1. Field of Invention
The present invention relates to a method of checking the condition of an inkjet printhead. More particularly, the present invention relates to an inkjet printhead chip structure and a method of estimating the working life through the detection of any defect in the chip structure.
2. Description of Related Art
Inkjet printers are now widely used at home and in the office. The inkjet printhead is an expendable product in printing. In the fabrication of inkjet printhead, the fabrication of the chip is regarded as a front-end process. To obtain a complete printhead, the chip is combined with other components fabricated in the back-end processes. Simple and accurate assessment of the quality of the chip is important because the quality of the inkjet printhead largely depends on the quality of the chip. The production of high-quality printhead is able to reduce cost and unnecessary waste. Two recent trends regarding the use of inkjet printer are the recycling of inkjet printhead and the refilling of empty ink cartridge by the user. Due to such trends, the chip embedded in the inkjet printhead is more likely to be used until the end of its life span. Using such a mode of operation, a method of whenever if necessary, simply and accurately estimating working life of a printhead has great benefits. By the estimation of working life of the printhead, the printhead can be changed in time prior to the actual breakdown of the chip. Therefore, printing waste can be reduced considerably.
The chip embedded inside an inkjet printhead is normally formed using a brittle substance such as silicon. Hence, when the printhead is subsequently processed to form an ink slot, the silicon chip cracks along the direction of the ink slot. In general, the working life of the silicon chip is estimated by the degree of aging of a metal protective layer attached to the inkjet printhead. The metal protective layer will age because small amounts of residual ink bubbles may collapse to the metal surface every time printing is conducted, thereby causing corrosive chemical reactions.
FIG. 1 is a top view showing a conventional an inkjet printhead with a silicon chip thereon. As shown in FIG. 1, the inkjet printhead 100 has a rectangular appearance. A long and narrow ink slot 108 is positioned in the middle of the inkjet printhead 100. The inkjet printhead 100 is divided into two sections along its longitudinal axis. Each section includes a group of conductive lines 102 having a comb shape. A heating element 106 is installed at the junction near the root of the comb teeth. In other words, the heating elements 106 are aligned on each side parallel to the long and narrow ink slot 108. An insulated passivation layer (not shown) covers the heating element 106. On top of it, a metal protective layer 104 is formed over the heating elements 106. The metal protective layer 104 is made from a refractory metal such as tantalum.
According to the inkjet printhead shown in FIG. 1, the circuit on each side of the ink slot 108 is independently insulated. Hence, any crack 110 in the silicon chip running along the direction of the ink slot 108 remains undetected. There are two conventional methods of inspecting the condition of the inkjet printhead 100. One method makes use of an imaging system for detection of cracks in the silicon chip. The other method depends on dismantling the silicon chip from the inkjet printhead 100 to investigate the metal protective layer 104 above the heating elements 106 through a microscope. By observing clues such as color changes in the metal protective layer, the degree of aging of the silicon chip is estimable.
However, the detection of cracks in the silicon chip by an imaging system and the investigation of aging in the silicon chip in a destructive testing are time-consuming and tend to reduce product yield. On the other hand, if defective chips are not singled out in time, defective chips are incorporated into the inkjet printhead resulting in a waste in back-stage processing time. Furthermore, if these defective chips are left undetected so that these inferior quality products are sent to customers, the printing quality of the printers deteriorates much faster than expected, thereby tarnishing the product quality of the manufacturer. Moreover, microscopic investigation of the silicon chip requires dissembling the printhead. Therefore, the investigation is only carried out on a few samples in order to maintain a definite quality level in quality management.
Accordingly, one object of the present invention is to provide an inkjet printhead chip structure and a method for estimating the working life through the detection of any defect on the chip structure. The method includes laying a circuit over the chip such that resistance of this circuit is measured through contact regions at both ends of the circuit. The circuit is isolated from other working circuits so that operation of the printhead is unaffected. By measuring the resistance of the circuit, cracks on the chip are easily detected.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an inkjet printhead chip structure and a method for estimating the working life through the detection of any defect on the chip structure. The method includes laying a circuit over the chip. The resistance of this circuit is measured through a flexible circuit board. The circuit is isolated from other working circuits so that operation of the printhead is unaffected. By measuring the resistance of the circuit, any cracks on the chip are easily detected. Since a flexible circuit board is used to measure the resistance of the metal protective layer in an inkjet printhead, the measurement is conducted during manufacturing. Furthermore, this method is used to estimate the working life of the used inkjet printhead.
The invention provides an inkjet printhead chip structure and a method for estimating the working life through the detection of any defect on the chip structure. The method includes laying a circuit over the chip. The circuit is a metal protective layer formed over the chip using a material such as tantalum instead of aluminum. A portion of the metal protective layer covers heating elements on the printhead. In normal operations, the heating elements provide the heat necessary for forming high-temperature ink bubbles for printing. However, a portion of the heat is transferred to the metal protective layer on top, thereby raising its temperature. Meanwhile, a portion of residual ink bubbles may collapse onto the surface of the metal protective layer. Heat combined with chemical reaction with the collapsed ink thus ages the metal protective layer. Since resistance of the metal protective layer depends on the amount of aging, the degree of aging is determinable by resistance measurement. Hence, the working life of an inkjet printhead is predictable.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.